1. Field of the Invention
The invention relates to a lamp socket or holder for multipin lamps with spring-biased contacts for contacting the contact pins of a lamp, and a housing which in the final assembly state at least partially surrounds the lamp base of the lamp, wherein the housing is composed of an upper housing part which supports a device for aligning and securing the lamp, and a bottom hosing part which supports at least indirectly receiving means for the contacts.
2. Description of the Related Art
Lamp sockets of the above-described type are frequently used for securing and electrically contacting lamps in various lighting devices. In addition to the lamp and socket, these lighting devices frequently also include reflecting and/or refracting optical systems of various complexity which are optimized for the respective purpose of use. It is of particular importance in this connection that the actual incandescent filament is positioned in a well defined spatial relationship relative to the surrounding optical system. In a predominant number of cases, a manual adjustment of the incandescent filament and/or the optical system adapted to each individual case is not possible. Rather, most manufacturers construct the lamps in such a way that the incandescent filament has a precisely specified alignment relative to a contact surface or contact line at the lamp base. Consequently, the sockets which are usually fixed relative to the optical lighting system have in most cases a corresponding reference surface whose purpose it is to ensure an automatic alignment of the lamp, for example, by biasing the lamp base relative to the reference surface by a spring.
However, a more fundamental purpose of the lamp socket is to provide a secure electrical contact of the contact pins which must be ensured even at high temperatures and after frequent replacements of the lamp.
In order to meet this object, various solutions have been proposed. Sockets are known in the art which, among other features, include a ceramic bottom housing part which is provided with recesses for inserting the contact pins. One of these recesses is usually tapered in the shape of a prism, wherein a spring-biased contact plate is arranged opposite the prism-shaped taper so that the inserted contact pin is pressed by the contact plate into the prism-shaped groove and the contact pin is secured relative to the bottom housing part as a result. Additional contact pins are secured in a similar manner, wherein, however, manufacturing tolerances must frequently be taken into consideration by providing the recesses with the shape of oblong holes.
However, this results in the decisive disadvantage that two pairs of reference are defined, i.e., the lamp base and the upper housing part, on the one hand, and the contact pin and the upper housing part, on the other hand, wherein the relative alignment of the contact surface or line at the lamp base relative to those at the contact pins is not specified and is usually subject to significant manufacturing tolerances. At which pair of reference the alignment actually takes place depends essentially on the dimensioning of the spring forces which, however, may also be subject to variations due to temperature changes.
Another disadvantage is the fact that, when the alignment takes place at the contact surface provided by the lamp manufacturer, contacting of the contact pins can only be optimized in exceptional cases. Especially in the case of higher temperatures, this results in contacting problems which significantly reduces the reliability of the entire lighting device.
A contacting device which is supposed to eliminate this disadvantage is disclosed in DE 295 19 948.2. In that case, the contact is provided by two shaped parts which engage in each other in an articulated manner, wherein the shaped parts form together a receiving means for a contact pin on one side of the point of engagement between the shaped parts, and wherein the shaped parts include a helical spring on the other side of the point of engagement, and wherein the helical spring produces a resilient force acting against the expansion of the receiving means as a result of the insertion of the contact pin. The entire contact unit is movably mounted in a plane extending perpendicularly of the desired position of the contact pins, so that the position of the contacts can adapt to the respective position of the contact pins. No force acts on the lamp base proper, so that a defined alignment at the contact surface of the lamp base and the corresponding reference surface of the lamp socket becomes possible. However, this device has the disadvantage that the contacts are complicated and expensive to manufacture, and that there is no possibility for an adjustment to contact pins which are in an inclined position. Moreover, the contacts must be manufactured of an electrically conductive material, which makes it necessary that the contacts are embedded in a ceramic socket base; because of the moveable support, the socket base must be constructed of two parts which results in additional costs.
In accordance with another solution known in the art, individual contacts are provided for each contact pin, wherein the contacts have a cylindrical shape which corresponds to the contact pins. The contacts are manufactured from a base plate with several tongues, wherein the tongues are bent perpendicularly relative to the base plate and are at their upper ends connected to a spring ring. This results in a cup-shaped structure which is inserted in a ceramic housing base, wherein a contact pin each is placed in the cup-shaped structure. However, this solution has significant disadvantages. The diameter of the opening of the contact cup can be expanded elastically only to a minimal extent, so that the sometimes significant tolerances in the diameters of the contact pins can be compensated only insufficiently. Consequently, particularly in the case of high temperatures, incorrect contacting frequently occurs. Moreover, only a restricted mobility of the contact cups relative to the ceramic socket base can be realized because the contact pin must be inserted very precisely into the opening of the cup in order to ensure that the contact pin does not slide next to the cup and destroys it. This results in an insufficient positional alignment of the contacts relative to the contact pins. Finally, it is also in this solution absolutely necessary to provide an electrically insulating housing base with guide means for the contact pins, so that particularly inclined positions of the contact pins can be compensated only insufficiently.